EP0065459A1 - Process and apparatus for feeding a gas generator - Google Patents

Abstract

Method and device for the supply of pulverized fuel material to a gas generator comprised by a vessel (1) maintained under pressure wherein are injected a combustive fluid, a moderator fluid, and a mixture (8) containing a solid carbonaceous fuel reduced to powder, that is introduced in the vessel of the reactor by means of a screw conveyor forming at the inlet of the vessel (1) a plug (80) of compressed material tight to the pressure of the reactor (1) and continuously renewed as it is introduced. According to the invention, for the driving and compression of the mixture (8) introduced in the vessel, by using at least two screws (2, 3) intermeshed, with similar helical threads, rotatingly driven in the same direction inside a sleeve (4) which envelopes them, the pressure-tight plug of compressed material introduced in the pressure vessel (1) contains at least 85 % of solid material and remains friable when entering the vessel (1) of the reactor.

Description

The subject of the invention is a method and a device for supplying a gas generator consisting of a pressure vessel into which a solid carbonaceous fuel is injected in spray form, a moderating fluid and a fluid containing for example l 'oxygen.

Generators producing gas from solid carbonaceous fuels such as pulverized coal must normally be put under a pressure of the order of 10 to 80 bars to have a correct efficiency. The fuel previously ground to a fairly fine particle size, of the order of 0.5 mm, is injected into the enclosure which also receives an injection of oxygen, the assembly constituting a gasification reactor.

Furthermore, in this type of process, the gasification of the fuel risks leading to excessively high temperatures and this is why, usually, a moderating fluid is used with the fuel. dissipate the amount of excess heat.

The introduction of a solid material sprayed into a pressure vessel is obviously difficult.

It has been proposed for this purpose to use a briquetting press comprising a piston which compresses the solid fuel in a conduit opening into the reactor. In this case, the fuel supply takes place discontinuously, which can present a drawback for adjusting the operation of the generator. In a known process to which the invention particularly applies, the pulverized coal is suspended in a liquid. A pumpable mixture is thus obtained which makes it possible to use mud pumps of known type for the supply of the generator. However, these pumps only work for pasty suspensions containing a part by weight of liquid phase generally between 30 and 60%. Generally, this liquid phase is water, which also plays the role of the moderating fluid, the need for which was recalled above. However, when the moderating fluid is water, the optimal proportion to be introduced into the reactor is generally of the order of only 15% and, by exceeding this proportion, the thermal yield of the reaction is obviously reduced. It is therefore interesting to reduce as much as possible the amount of water used for transporting the fuel.

To achieve a continuous supply of the reactor under sufficient pressure while limiting the water content of the pasty material in For this purpose, it has also been proposed to use a screw conveyor supplied upstream with a mixture of fuel and water and provided with a die at the downstream end opening into the reactor and in which extrusion is formed. a plug of compressed material tight to the preæion of the enclosure and continuously renewed as it is introduced into the reactor. An extrusion press can be used for this purpose, comprising a single helical screw driven in rotation inside a sheath provided at its downstream end with a hollow conical part forming a convergent and opening into the reactor vessel. gasification by an orifice forming a die in which the material entrained by the screw is compressed until formation, at the outlet, of a plug which is sealed to the pressure of the reactor.

With such presses, the desired pressures can be obtained with mixtures containing less than 40% liquid. However, one cannot, in practice, reduce the quantity of water below 20% because a minimum quantity of water is necessary to obtain the rise in pressure and the formation of a tight plug. In fact, in single-screw presses, the material can be transported only if it completely occupies the threads so as to exert friction against the internal wall of the sheath which prevents it from turning around the screw shaft. It has been observed that a solid material, in particular pulverulent material, can only be entrained by a screw and, all the more reason, compressed only if it is associated with a liquid phase to form a pasty mixture. On the other hand, if the pressure increases too much, the water which escapes from the solid matter forms a film along the sheath which reduces friction and consequently the effect of entrainment downstream of the matter , the extruder throughput quickly becoming zero. Thus, a conveyor with a screw does not work well and allows a plug to be obtained at the desired pressure only for a mixture of a solid phase and a liquid phase in proportions determined with sufficient precision. On the other hand, because the entrainment of the material occurs essentially in a longitudinal direction, there may exist in the threads less filled areas and it is necessary to achieve a homogenization of the material at the outlet of the threads and before entering the die, that is to say, normally, in the convergent placed at the end of the sheath to direct the materials towards the die and into which the conical point of the screw penetrates. This can be provided, for example, with spikes which loosen the material to bring it back to the pulverulent state, but which are subjected to significant wear.

To overcome this drawback, it has been proposed to use for the introduction of the material a conveyor with two screws fed by the pulverulent material and by a certain quantity of liquid, the effect of meshing of the screws ensuring the homogenization of the mixed. The sheath opens at its outlet in a long enough duct to produce, by braking the material, a compression of the latter until the formation of a pressure-tight plug prevailing inside the enclosure of the generator. In all cases, a very compact rod of materials is therefore introduced into the enclosure, which must however be disintegrated as soon as it enters the reactor. It is therefore necessary to maintain inside this tube a certain amount of liquid phase which, on entering the reactor, vaporizes under the effect of the sudden rise in temperature and thus produces the disintegration of the tube. If the quantity of liquid phase is not sufficient, however, there is a risk that, since the disintegration does not take place under good conditions, compact pieces of relatively large dimensions are introduced into the reactor.

Thus, in all the cases known up to now, when using a screw conveyor, the continuous plug necessary to ensure the seal is formed in a single conduit placed at the outlet of the screws and it must contain a certain amount , generally important, of liquid phase.

However, in the case of an industrial gasification reactor, the quality of the fuel mixture supplied upstream of the extruder and in particular its water content can vary in fairly large proportions. The influence of the water content of the fuel is obviously greater the lower the total water content of the mixture and this is also a reason why it is necessary to supply the reactor with relatively wet mixtures, containing at least 30 to 40% water.

The subject of the invention is a new supply method making it possible to remedy these various drawbacks and bringing other important advantages. The invention also relates to a supply device specially adapted to the implementation of the method.

In accordance with the invention, the plug of compressed material introduced into the pressure vessel contains a determined quantity which may be zero in the liquid phase, and, if necessary, a complementary flow of moderating fluid is injected separately into the reactor in order to reach the total quantity necessary for the optimal thermal balance of the reactor.

On the other hand, in a particular embodiment of the invention, the screw conveyor is supplied with a wet mixture containing a proportion of liquid phase greater than the optimum content and this mixture is wrung during compression of the material for the formation of the tight plug, the excess amount of liquid phase being discharged through a filtering zone formed in the sheath of the screw conveyor, upstream of the zone of formation of the plug.

According to another important characteristic, the pressure of the compressed material in the plug is measured and the feed rate of material in the extruder and the speed of rotation of the screws are adjusted so as to maintain a corresponding determined pressure in the plug. at the desired liquid phase content, said pressure being greater than the reactor pressure.

The constitution of a sufficiently tight plug from a material that can be dried is permitted in particular by the use of a conveyor with identical screws driven in rotation in the same direction and comprising at least two successive zones with threads of different pitch, respectively a zone with direct pitch threads for downstream transport followed by a zone with reverse pitch threads which constitutes the braking zone, the watertight stopper being produced in this zone, inside the sheath. The material is driven partially in rotation around the screws in the transport zone and therefore undergoes progressive compaction with pressure build-up until the threads are completely filled in the zone with inverted pitch, the sealing being ensured in this area by the screws themselves and by the material compressed in the threads and against the sheath. The passage downstream of a determined flow of material with maintenance of the seal is ensured by spaced openings formed in the threads not inverted.

The device used especially for the implementation of the method according to the invention therefore consists of a screw conveyor comprising two identical thread screws driven in rotation in the same direction, the sheath being provided at its downstream end with two outlet orifices placed respectively in the axis of each dosais at the tip of two convergers into which the conical ends of the two screws penetrate.

According to a particular embodiment of the method, a slight decompression of the material is carried out in the two convergers with the start of disintegration and the material is directly introduced into the generator enclosure by the two orifices each placed in the axis of a screw.

• La figure 1 est une vue en élévation et en coupe axiale du dispositif d'alimentation selon l'invention.
• La figure 2 est une vue en coupe transversale selon II-II, figure 1.
• La figure 3 est une vue en coupe axiale d'un mode de réalisation plus perfectionné du dispositif d'alimentation selon l'invention.

The invention will be better understood by referring, by way of example, to a particular embodiment shown in the accompanying drawings.

• Figure 1 is an elevational view in axial section of the supply device according to the invention.
• Figure 2 is a cross-sectional view along II-II, Figure 1.
• Figure 3 is an axial sectional view of a more improved embodiment of the supply device according to the invention.

In Figure 1, there is shown schematically the enclosure 1 of the gasification reactor at the top of which is placed the supply device.

This consists of a transporter comprising two parallel screws 2 and 3 meshing one inside the other and placed inside a sheath 4 which envelops them. Preferably, the two screws are identical and driven in rotation in the same direction by a motor 5.

The rotation of the two screws determines the drive from upstream to downstream (that is to say, in the example shown, from top to bottom) of the material 8 introduced by an inlet orifice 51 to which is connected a supply device not shown, for example a pipe supplied by a slurry pump.

The downstream end of the sleeve 4 opens out inside the enclosure 1 and is preferably provided with two outlet orifices 42, 43 each placed in the axis of a screw 2, 3, at the outlet of a conical part 44, 45 forming a convergent and inside which a point 21, 31 formed at the end of each screw 2, 3 penetrates.

Along the sheath are formed oxygen supply conduits 6 which open into the enclosure 1 and are directed towards the strands of material 80 leaving the two orifices 42, 43. It has been found that the use of an extruder with several screws driven in rotation in the same direction and emerging through several orifices in the enclosure 1 makes it possible to supply the latter with a solid powder mixture whose content in liquid phase can be reduced to a minimum and even, depending on the nature of the combustible, be zero.

Indeed, in a machine with two screws, as shown in FIG. 2, the material 8 is entrained by the threads of the two screws around them following the walls of the sheath 4, according to the arrows 40 of Figure 2. Although made of a powder with a fine grain size, the material can thus be entrained downstream even when the nets are not completely filled. Inside each thread, the material rotates around the shafts 20 and 30 and must overcome resistance when it arrives in the engagement zone A where the space between the threads of the screw 3 is occupied by a thread of the screw 2 and vice versa in part B, of each thread of the screw 3. This results, upstream of the engagement zone A, of an accumulation of material B1 which compresses then expands when it passes through part C ₂ of the corresponding thread of screw 2. It then turns around the shaft 20 of screw 2 and again compresses in part B ₂ upstream of the engagement zone A before passing into part C ₁ of the next thread of screw 3.

As the screws advance, the material thus passes, from one thread to another, through a succession of compression phases B and expansion C which favor the compaction and possibly a crushing effect of the solid particles. The importance of the compressed zones B increases as the advance downstream and, when one arrives near the exit of the extruder, the threads are completely filled.

Thus, at the end of its transport in the screws, and in particular if the material has been braked by threads with a tight pitch, the material is perfectly distributed and compacted all around the screws and the sealed zone D covers not only the outlet and converging but also the last two or three threads of the screws which are completely filled with compressed material. Sufficient sealing can thus be obtained even with a relatively dry material. It should also be noted that the carbonaceous nature of the fuel promotes the obtaining of a sufficient seal and the transport of dry matter.

On the other hand, an outlet orifice 42, 43 has been placed in the axis of each screw and consequently, for a given feed rate, each outlet orifice 42, 43 has a smaller section than that of the he single orifice of a single screw and the seal is more easily maintained there.

Thus, one exits through the orifices 42, 43 two tight tubes of material 80 which, although strongly compressed, remain brittle due to the low degree of humidity and easily disintegrate as soon as the pressure is no longer exerted, at the outlet of the orifices 42, 43 and in particular under the action of gas jets 61 supplied by the pipes 6.

It is thus possible to introduce into the gasification reactor a material whose moisture content is, for example, between 5 and 15% but can be further reduced if necessary. This results in a very important advantage in a gasification reactor because, precisely, when the moderating fluid is water, the optimal amount for satisfactory operation of the reactor is of the order of 15% of liquid relative to the total weight. of material introduced. Thus, we only introduce pra no excess water and the thermal balance of the reactor is significantly improved.

Such a conveyor with two screws therefore makes it possible to introduce with the combustible material a minimum quantity of water, possibly less than the optimal quantity and to inject separately into the reactor an additional flow of water or of moderating fluid so as to maintain at any time in the reactor the amount of moderator just necessary for the proper functioning of the reaction.

Thus, thanks to the arrangements according to the invention, it is possible to permanently adjust the quantity of water or moderating fluid introduced into the reactor to the optimum proportion.

Moreover, the possibility of introducing the fuel into the reactor with a minimum content of liquid also makes it possible to use a moderating fluid different from the liquid introduced with the fuel.

For example, the moderating fluid can be evaporated and / or preheated to be introduced in the form of hot gas under pressure, possibly in the jets (61) for disintegrating the rod of solid material.

The production of the plug of compressed material inside the sheath 4 is carried out under even better conditions if a machine with several screws of the type shown in FIG. 3 is used.

In this case, the transport zone G provided with threads with direct downstream drive steps is followed by a zone H comprising two or three threads with inverted steps which therefore produce more effective braking of the material and consequently a significant increase in pressure. To allow the passage downstream of a certain flow of material, the threads 23 are provided with windows 24 constituted by spaced openings, formed radially between the shaft of the screw and the periphery of the thread. The screws, which are identical and rotated in the same direction, are wedged so that the openings 24 and 34 of the threads placed side by side on the screws ₂ and ₃ come simultaneously into coincidence in the interpenetration zone A. Thus, the material compressed inside the threads 23 and 33 is and pushed by the entrained material downstream in the transport zones G / can pass downstream through this central window which opens and closes at periodic intervals, the passage of a thread to the next of the same 5 screws can also be done by the other windows 24. This controls the passage downstream of a certain flow of material while maintaining the seal since zone H is completely filled with matter.

In this zone, the sealing is therefore carried out by the screws themselves. same and by the material which completely fills the threads and is applied under strong pressure against the walls of the sheath so as to fill the slight gap existing between the periphery of the threads and the internal wall of the sheath 4. The pressure is therefore exerted on the entire internal surface of the sheath and the sealing must only be ensured on the perimeter of the screws, the interpenetration zone A being perfectly filled because the screws are rotated in the same direction.

Furthermore, as shown in FIG. 3, it is also possible to provide the screws with several successive pairs of associated zones, respectively of transport G and of braking H so that sealing can be ensured in the braking zones H and H '.

A particular advantage of this arrangement is the fact that, since the seal is sufficiently ensured in the zones with inverted steps, it is possible to allow the material to decompress slightly when it passes through the two convergers 45 and the two dies. 42 and 43. In the two convergers, the material leaving the threads and slightly decompressed can be partially entrained around the screws and this rotation, associated with the passage through the convergers and the dies, can produce the start of disintegration of the tight plug.

Thus, thanks to these improved feed devices, it is possible to introduce into the reactor a practically dry material which crumbles easily under the action of the jets 61.

However, the use as a feeder of a twin-screw extruder has other advantages in the case of a gasification reactor. In fact, it has been found that the operation of the conveyor with two screws and in particular the flow of material obtained at the outlet and the pressure reached depends very little on the composition of the mixture and in particular on the proportion of dry matter which can range, for example, from 5 at 60% whereas a single screw extruder only works satisfactorily for a composition defined in fairly precise proportions. Therefore, the operation of the feed device is less dependent on variations in composition and in particular in water content of the coal. This is also one of the reasons why a much drier mixture can be used.

The invention therefore gives the important advantage of allowing the use in the gasification reactor of coals of any kind.

In fact, as indicated, to obtain an attractive yield from the gasification reactor, it is preferable that the material com bustible introduced therein has a fairly limited water content and preferably less than 15%. However, for the determination of this water content, only the combustible part of the solid material introduced must be taken into account. Consequently, if the solid matter contains a certain proportion of incombustible ash or pore water, as in the case of lignites the ratio of the proportion of useful combustible material, to the proportion of water, is further reduced.

If, for example, the fuel introduced into the reactor consists of coal containing 30% of non-combustible ash, the use of a conveyor with several screws makes it possible to produce and introduce into the reactor a tight plug containing only one proportion of interstitial water of 10% which corresponds to the quantity of moderating fluid required, taking into account the proportion of carbon contained in the mixture.

If the fuel is a lignite containing, for example 20% of water of constitution, this quantity is already sufficient for the moderation of the reaction and, thanks to the use of an introduction machine with several screws, it is avoided to add still water for the transport of the material, this being introduced dry in the reactor.

Thus, thanks to the possibility, according to the invention, of supplying the reactor with a combustible mixture whose liquid phase content can be reduced to a minimum and even practically zero, the quantity of liquid can be added to the solid material, and in particular water, just necessary for the proper functioning of the reaction as a function of the useful quantity of combustible material introduced, taking into account the proportion of ash and chemically bound water.

On the other hand, it has been observed that there is a relationship between the water content of the mixture and the pressure which is obtained in the convergers 44, 45 and in the outlet orifices 42, 43 of the screws. Consequently, according to the flow of material which it is desired to obtain at the outlet of the device, it is possible to adjust) as a function of one another, the flow of supply of mixture to the inlet orifice 41 and the speed of rotation of the screws so as to maintain the pressure inside the tight plug at a substantially constant value corresponding to the water content of the mixture at the outlet 42, 43 of the sleeve.

To be sure of ensuring a sufficient seal, it will therefore be possible to place in the sleeve 4, in one of the outlet orifices 42, 43 or in a convergent, a pressure sensor 7, connected to an indicator 70 which will make it possible to verify at any time that the pressure at the outlet of the extru deuse remains greater than the pressure P inside the enclosure 1, with the desired safety coefficient. If the pressure varies, it will be brought back to the desired value by modifying the feed rate at the inlet 41 of the extruder to adjust the filling rate of the screws and / or by varying the speed of rotation of the screws. This adjustment is done quite easily because, in a twin screw extruder, the action on the compression ratio is faster than in a twin screw extruder and, for a relatively constant water content, the pressure reached at the outlet remains fairly stable.

In addition, the use of a conveyor with several screws has the advantage of allowing a variation in the flow of materials at the outlet of the sheath 4 in a fairly large proportion without substantially modifying the pressure in the dies 42, 43. Thus, while ensuring the desired tightness, the flow rate can be varied as a function of the operating conditions of the reactor, this adjustment therefore being more flexible than in the case where the reactor is supplied by an extruder with a single outlet.

To obtain a low and even zero water content in the plug of compressed material introduced into the reactor, it is obviously possible to adjust the proportions of liquid phase and solid phase in the mixture introduced through the inlet orifice to the desired value. of the screw conveyor. Moreover, in the installations known up to now, these proportions were not modified during the transport and the compression of the material before it entered the reactor.

However, according to an additional and important characteristic of the invention, it is possible, thanks to the use of a conveyor with several vi3, to carry out a wringing of the combustible material during its compression and, consequently, of lower the water content of the material introduced to the desired value even when the mixture supplied by the inlet orifice 41 contains a large proportion of liquid.

To this end, filtering parts 46 are housed on the sheath 4 in the zone E which precedes the braking and compression zone D where the threads are completely filled; there is then a separation of the solid phase which is entrained towards the avagtjde the liquid phase which can rise upstream and escape through the filtering zones. Indeed, as indicated, the threads are not completely filled at the start of the screws, and the compression of the solid matter entrained around the screws in part B of each thread before the meshing zone, causes the expulsion of 'a certain amount of water which remains in the relaxed zone C of the net. As the relaxed zones C of the threads of the same screw are placed in the same sector an gular of the screw, the liquid phase can rise from one thread to the other, passing in the clearance necessarily existing between the screw and the sheath, up to the filtering zone E where it is discharged.

On the other hand, it has been indicated that, for a determined flow of material at the outlet of the extruder, the pressure in the outlet orifices 42 and 43 is linked to the water content and that if one adjusts, as as mentioned above, the feed rate and the speed of rotation of the screws to keep the pressure constant in the orifices 42 and 43, the water content of the material leaving the extruder also remains constant, the quantity excess escaping through the filtering part 46 of the sleeve.

Consequently, it is possible, in this case, to feed the extruder with a mixture containing a high proportion of water, for example a suspension at 40% of dry matter, and in spite of everything obtain a wrung material at the outlet of the extruder. up to a relatively constant water content which can be less than 15%. However, it is very important for proper operation of the reactor to control the water content of the fuel introduced into the enclosure 1 whatever the variations in composition of the suspension arriving via the supply line in the inlet orifice 41 .

Finally, the use, in the embodiment of FIG. 3, of inverted pitch threads provided with windows to produce the sealed plug inside the sheath gives the possibility of feeding the screw conveyor with a material consisting of particles of extended particle size, for example up to several millimeters. In this case, in fact, the packing carried out in the downstream part of the transport zone makes it possible to obtain a tight stopper even with pieces of various dimensions. In addition, the passage in the zones with inverted pitch achieves a fragmentation of the material, the windows allowing only downstream passage of the particles not exceeding a given dimension. This fragmentation can also be spread over several spaced braking zones, as in the case of FIG. 3, the width of the windows being able to decrease from upstream to downstream.

Of course, the invention is not limited to the embodiment which has just been described, and which could be the subject of variants,

This is how one could, if necessary, use more than two feed screws.

On the other hand, if, as indicated above, it is preferable to place a hole 42, 43 in front of each 2, 3 "screw, we could also make a single compressed plug in a single outlet orifice placed at the outlet of a convergent including the ends of the two screws.

On the other hand, nn has shown an extruder with a vertical axis, but one could also place the axes of the screws in a horizontal plane in particular to facilitate the evacuation of the water in the case where a wringing is carried out by parts sheath filters.

Claims (9)

1.- Method of supplying combustible material to a gas generator consisting of an enclosure (1) maintained under pressure, into which are introduced a mixture containing a solid carbonaceous fuel reduced to particles, an oxidizing fluid and a fluid moderator, the combustible mixture being introduced into the reactor enclosure by means of a screw conveyor comprising at least two parallel screws driven in rotation inside a sheath (4), the combustible mixture (8) introduced into an upstream end of the sheath (4) by an inlet orifice (41) being driven downstream by the rotation of the screws then passing through a braking zone which determines a compression of the material and the formation of a plug ( 80) of compressed material impervious to the pressure prevailing in the enclosure (1) of the generator and continuously renewed as it is introduced therein, characterized by the fact that the plug (8 ₀ ) of compressed material introduced into the enclosure under pres sion contains a determined quantity which may be zero in the liquid phase and which, if necessary, is injected separately into the reactor with an additional flow rate of moderating fluid to reach the total quantity necessary for the optimum thermal balance of the reactor. 2.- feeding method according to claim 1, characterized in that one feeds the screw conveyor in urmix containing a certain proportion of liquid phase and that one carries out a wringing of this mixture during compression material for the formation of a tight plug (80), containing a determined proportion of liquid phase, the excess quantity being evacuated by a filtering zone (46) formed in the sheath (4) upstream of the zone (D) plug formation. 3.- Feeding method according to one of the preceding claims, characterized in that the pressure of the material compressed in the plug (80) is measured and that the flow rate of material is adjusted. the extruder (4) and the speed of rotation of the screws (2, 3) so as to maintain in the plug (80) a determined pressure corresponding to the desired liquid phase content, said pressure being greater than the pressure in the enclosure (1) of the reactor. 4.- A method of supplying a gas generator according to claim 1, characterized in that, thanks to the use of a conveyor with identical screws driven in rotation in the same direction and comprising at least one pair of areas with different pitch threads, respec tively a zone with direct pitch threads for downstream transport followed by a zone with inverted pitch threads constituting the braking zone, the tight plug (80) is produced in this zone, inside the sheath (4 ), the material being driven partially in rotation around the screws in the transport zone and undergoing a progressive compaction with pressure build up until the threads are completely filled in the zone with inverted pitch in which the sealing is ensured by the screws themselves and by the material compressed in the threads and against the sheath, the passage downstream of a determined flow of material with maintenance of the seal being ensured by spaced openings made in the threads with inverted pitch . 5.- Feeding method according to claim 4, characterized in that, each screw being provided, immediately downstream of the inverted pitch zone, with a point penetrating into a convergent, a slight light is produced in the two convergent decompression of the material with the start of disintegration and the material is introduced directly into the enclosure (1) of the generator by orifices each placed at the tip of a convergent in the axis of the screw. 6.- feeding method according to claim 4, characterized in that the material introduced at the inlet (41) of the sheath (4) consisted of particles of different particle sizes, fragmentation of the material particles is carried out during packing and compression inside the sheath to a degree of fineness determined by the size of the openings of the zone with inverted pitch. 7.- Device for supplying combustible material to a gas generator, constituted by a conveyor with several screws comprising at least two parallel screws (2 and 3) driven in rotation inside a sheath (4) la material introduced through an inlet orifice (41) of the sleeve (4) being driven downstream by the screws and passing through a braking zone (D) where a plug (80) of compressed material is formed which is impermeable to the prevailing pressure in the generator and continuously renewed as it is introduced therein, characterized in that the two screws have identical threads and are rotated in the same direction and that the sleeve (4) is provided at its end downstream of two outlet orifices (42, 43) placed respectively in the axis of each of the screws (2, 3) at the tip of two convergers (44,45) into which the conical ends (21, 31) of the two penetrate screws (2, 3). 8.- Feeding device according to claim 7, characterized in that the elongated sheath (4) is provided upstream of the compression zone (D) with a wringing zone (E) comprising filtering parts ( 46) for the evacuation of the excess quantity of liquid phase. 9.- Feeding device according to claim 7, characterized in that the two screws (2, 3) comprise, from upstream to downstream, at least two zones with threads of different pitch, respectively a zone with direct downstream transport threads and an area of inverted pitch braking of the material for the constitution in the threads of the plug (80) of compressed material, the inverted threads being provided with spaced openings s 'extending radially between the shaft and the periphery of the screw, for the downstream passage of a determined flow of material with maintenance of the seal.

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